Solid-phase synthesis and biological activity of a combinatorial cross-conjugated dienone library

The solid-phase synthesis of a combinatorial cross-conjugated dienone library based on the structure of clavulones and their biological activity are reported. Clavulones are a family of marine prostanoids, and are composed of a cross-conjugated dienone system bearing two alkyl side-chains. The cross-conjugated dienone system irreversibly reacted with two nucleophiles. Our strategy for the solid-phase synthesis of the cross-conjugated dienones involves the Sonogashira-coupling reaction of a solid-supported cyclopentenone 10 bearing an acetylene group, followed by aldol condensation with aldehydes. The diphenyl derivative 7 aA was prepared from the solid-supported cyclopentenone 10 in 56% total yield. Combinatorial synthesis of a small library using twelve halides and eight aldehydes resulted in the production of 74 desired compounds from 98 candidates, and were detected by their mass spectra. Antiproliferative effects of the crude compounds against HeLaS3 cells showed that eleven samples showed strong antitumor activity (IC50<0.05 microM). Further biological examination of four purified compounds by using five tumor cell lines (A549, HeLaS3, MCF7, TMF1, and P388) revealed strong cytotoxicity comparable to that of adriamycin.     

Solid-phase synthesis of a tyrphostin ether library

The solid-phase synthesis of a 4500-member (30 x 15 x 10) tyrphostin library is demonstrated utilizing the Irori-directed sorting system. Fmoc-protected PL-Rink resin was used as the solid support. After Fmoc-deprotection, aryl aldehydes were attached to the resin through reductive amination. Acylation of the resulting secondary amines with cyanoacetic acid was followed by a Knoevenagel condensation with phenolic aldehydes. Mitsunobu coupling of primary alcohols to the resin-bound phenols yielded the final library of compounds 1.     

Solid-phase combinatorial synthesis of aeruginosin derivatives and their biological evaluation

A 24-member combinatorial library based on the structure of aeruginosin 298-A (1a) was synthesized utilizing solid-phase, and their inhibitory activity against trypsin was evaluated. Among the library, we found that D-Hpla-D-Leu-L-Choi-Agma (1h) is 300 times more potent than the parent natural product 1a.     

Solid-phase synthesis of a library of hydroxyproline derivatives

The synthesis of a library of N-alkylated O-arylated hydroxyproline derivatives has been achieved on solid phase. The choice of O-protection and the optimization of the Mitsunobu reaction involving a secondary alcohol were key to the success of this synthesis. First, acylation of resin-bound amines with N-Fmoc-O-THP-hydroxyproline was accomplished readily. Subsequent deprotection of the Fmoc and reductive amination with different aldehydes resulted in the tertiary amine intermediate. The deprotection of the THP group by p-toluenesulfonic acid was followed by a Mitsunobu reaction with a series of phenols. Finally, the products were cleaved from the resin using trifluoroacetic acid to produce a 10 200 member library.     

Solid-phase synthesis of a 4-substituted gamma-lactam library

Pyrrolidin-2-one (gamma-lactam) derivatives have shown a wide range of activities as ligands to diverse receptors, e.g., integrin, CCR5, and CCK. Therefore, we have prepared a large library of these derivatives for high-throughput screening against various protein targets, after developing a synthesis of pyrrolidin-2-ones on solid phase. Exploration of the ring formation was key to the success of this synthesis. First, acylation of resin-bound amines with N-Fmoc-protected amino acids and subsequent deprotection of the Fmoc group were accomplished readily. The resulting resin-bound primary amines were treated with beta-monomethyl itaconate under gentle heat in a mixture of methanol and toluene to yield the desired intermediates. Finally, saponification, amide formation, and cleavage from the resin led to the production of a library of 12,000 pyrrolidin-2-one derivatives. These products were isolated as diastereomeric mixtures of high purity and were obtained in good yields.     

Solid-phase synthesis of a thymidinyl dipeptide urea library

A thymidinyl dipeptide urea library with structural similarity to the nucleoside peptide class of antibiotics was designed and synthesized. To generate the library, a solid-phase synthesis was developed starting from 5'-azidothymidine attached to a polystyrene butyl diethylsilane (PS-DES) resin support. This study describes the prelibrary solid-phase synthesis development including maximum loading capacity optimization, selection of orthogonal functionalized side-chain protection strategies, synthesis of a 64-member test library, and optimization of the final cleavage step. Using the optimized procedures, we synthesized a 1000-member library in a 50 micromol quantity using IRORI-directed sorting technology in MiniKans, producing the target library in good yields and purity.     

Solid-phase synthesis of an isoxazolinopyrrole library

A four-step solid-phase synthesis of isoxazolinopyrroles 8 that employs an acid-labile 2-(4-formyl-3-methoxyphenoxy)ethyl polystyrene HL resin 1 is reported. Resin-bound vinyl sulfone 5 is obtained by DIC coupling with acid 4, which was in turn synthesized in solution phase by a regioselective nitrile oxide 1,3-dipolar cycloaddition. The resin-bound pyrrole 7 was synthesized on solid phase by pyrrole annulation with various isocyano derivatives and potassium t-butoxide in which the sulfone alpha-anion generated by Michael addition gives the desired pyrrole through internal condensation followed by a sigmatropic [1,5]-hydrogen shift. The resulting isoxazolinopyrroles 8 were released from resin 7 by 10% TFA in moderate to excellent overall yields from 2-(4-formyl-3-methoxyphenoxy)ethyl polystyrene HL resin 1.     

Solid-phase synthesis of an alkylaminobenzanilide library

The synthesis of a library of 2- and 3-substituted benzanilides has been achieved on solid phase. Attachment of anilines to formyldimethoxyphenyl (FDMP) resin via reductive amination was optimized to allow a wide range of anilines to be used. Acylation of this resin-bound aniline was accomplished with 2- or 3-nitrobenzoyl chloride to yield nitrobenzanilides. Following reduction of the nitro group, the resulting amine was alkylated using aromatic and heteroaromatic aldehydes in the presence of NaBH(OAc)(3) under controlled conditions. Finally, the products were cleaved from the resin using trifluoroacetic acid to produce a 10 800-member library.     

Solid-phase oligosaccharide synthesis of a small library of N-glycans

Solid-phase oligosaccharide synthesis is based on a hydroxymethylbenzyl benzoate spacer linker which is connected to the Merrifield resin (1 P). Glycosylation was performed with O-glycosyl trichloroacetimidates of glucosamine, mannose, and galactose permitting chain extension (2e, 5e), branching (4b, 7b, 8b), and chain termination (3t, 6t, 9t) with the use of O-benzyl, O-benzoyl, and N-dimethylmaleoyl as permanent and O-fluorenylmethoxycarbonyl (Fmoc) and O-phenoxyacetyl (PA) as temporary protecting groups. The steps required on solid phase are i) glycosylation under TMSOTf catalysis, ii) selective cleavage of the temporary protecting groups, Fmoc with NEt3 and PA with 0.5 equivalents of NaOMe in CH2Cl2/MeOH, and iii) product cleavage from the resin with 4.0 equivalents of NaOMe in CH2Cl2/MeOH and following O-acetylation for convenient product isolation. Thus a highly successful synthesis of a small library of seventeen N-glycan structures was made possible comprising the N-glycan pentasaccharide core structure 53 and two further chain extended hexa- and heptasaccharide N-glycans with a glucosamine or a lactosamine residue, respectively, which is attached to one of the mannose residues of the core structure (56 and 59).     

Solid-phase synthesis and biological evaluation of a teleocidin library--discovery of a selective PKCdelta down regulator

Protein kinaseC (PKC) is linked to the signal-induced modulation of a wide variety of cellular processes, such as growth, differentiation, secretion, apoptosis, and tumor development. The design and synthesis of small molecules that regulate these different cellular signaling systems is at the forefront of modern drug design. Herein we report a) an efficient method for the synthesis of indolactamV (6), a PKC activator, and its N13-des(methyl) analogues (19) using a regioselective organometallic transformation, a convenient aminomalonate derivative (10) to introduce the appropriate functionality and an enantiospecific enzymic hydrolysis as key steps; b) the use of this method in the first solid-phase synthesis of a teleocidin library modifying the N-13, C-12 and C-7 alkyl chains, and, therefore, producing a library of potential activators and/or inhibitors of PKC of the general structure (32); c) the activation of PKC by selected members of the library using a MARCKS translocation in vivo assay system; d) the observation that some of these analogues are nearly as effective as the natural PKC activators phorbol dibutyrate and (-)-indolactam V (6), and e) the observation that some of these analogues have different potential to induce down-regulation of members of the PKC gene family after chronic stimulation.     

Solid-phase synthesis of liquid crystalline isoxazole library

Combinatorial library of isoxazoles was prepared by 1,3-dipolar cycloaddition on solid support. p-Cyano derivatives showed nematic and/or smectic A phases. A bilayer smectic phase for 2h is proposed by the combination of molecular mechanics calculation and X-ray diffraction experiment.     

Solid-phase synthesis of a focused library of trypanothione reductase inhibitors

A focused library of inhibitors of the enzyme trypanothione reductase was prepared using solid-phase synthesis. The inhibitors were based on a previously identified, non-competitive, lead compound comprising of two Pmc (2,2,5,7,8-pentamethylchroman-6-sulfonyl) side-chain protected, N-capped arginine residues linked by a spermidine bridge. In total six protecting groups and four capping groups were used to generate a 24-membered library. All compounds bearing the 5-methoxyindole-3-acetic acid capping group were found to have good activity. The most potent inhibitor was observed to contain the Mtr (4-methoxy-2,3,6-trimethylbenzenesulphonyl) protecting group on the arginine residue, terminated with tryptophan as the capping group.     

Solid-phase synthesis of an oxalic acid amide library

Monoamides of oxalic acid are of interest as bioisosteric replacements for phosphate groups in the design of new enzyme inhibitors. Here, we have demonstrated the use of oxalic acid as a linker to the Wang resin to synthesize individual or libraries of phosphate biosteres. The highly reactive resin-bound acid chloride reacts with arylamines to yield resin-bound N-aryloxamic acids (oxanilic acids). This methodology is especially useful for the rapid synthesis of 2-(oxalylamino)benzoic acids (OBAs), because it can be utilized for library synthesis and eliminates the intermediate purification step necessary in solution-phase reactions. The products are cleaved off the resin with trifluoroacetic acid in dichloromethane in good yields.     

Solid-phase synthesis of a type II′ β-turn peptido-mimetic library

The solid-phase synthesis of a dipeptide derived 2-amino-3-oxohexahydroindolizino[8,7-b]indole-5-carboxylate system (IBTM) is described. The IBTM moiety is formed via a solid-phase mediated Pictet-Spengler reaction of N-terminal tryptophan and the 4-{N-[1-(4,4-dimethyl-2,6-dioxocyclohexylidene)-3-methylbutyl]amino}benzyl (Dmab) ester of Fmoc protected aspartic acid β-aldehyde followed by γ-lactamization. This synthesis allows the regio- and stereoselective incorporation of a dipeptide surrogate of type II′ β-turns. The procedure is easily adaptable to combinatorial synthesis and a 576-member library was synthesized.     

The synthesis and biological characterization of a ceramide library

A facile synthesis of a combinatorial ceramide library and their activities in the NF-kappaB pathway and in apoptosis induction/prevention were demonstrated. A novel NF-kappaB activating molecule was discovered among ceramide containing beta-galactose, and the structural requirements of ceramides for apoptosis induction was elucidated.     

Solid-phase combinatorial synthesis of a lysyl-tRNA synthetase (LysRS) inhibitory library

The solid-phase combinatorial synthesis of a new library with potential inhibitory activity against the cytoplasmic lysyl-tRNA synthetase (LysRS) isoform of Trypanosoma brucei is described. The library has been specifically designed to mimic the lysyl adenylate complex. The design was carried out by dividing the complex into four modular parts. Proline derivatives (cis-gamma-amino-L-proline or trans-gamma-hydroxy-L-proline) were chosen as central scaffolds. After primary screening, three compounds of the library caused in vitro inhibition of the tRNA aminoacylation reaction in the low micromolar range.     

Synthesis and biological evaluation of a beauveriolide analogue library

Synthesis of beauveriolide III (1b), which is an inhibitor of lipid droplet accumulation in macrophages, was achieved by solid-phase assembly of linear depsipeptide using a 2-chlorotrityl linker followed by solution-phase cyclization. On the basis of this strategy, a combinatorial library of beauveriolide analogues was carried out by radio frequency-encoded combinatorial chemistry. After automated purification using preparative reversed-phase HPLC, the library was tested for inhibitory activity of CE synthesis in macrophages to determine structure-activity relationships of beauveriolides. Among them, we found that diphenyl derivative 7{9,1} is 10 times more potent than 1b.     

Solid-phase synthesis of bleomycin group antibiotics. Construction of a 108-member deglycobleomycin library

The bleomycins (BLMs) are structurally related glycopeptide antibiotics isolated from Streptomyces verticillus that mediate the sequence-selective oxidative damage of DNA and RNA. Deglycobleomycin, which lacks the carbohydrate moiety, cleaves DNA analogously to bleomycin itself, albeit less potently, and has been used successfully for analyzing the functional domains of bleomycin. Although structural modifications to bleomycin and deglycobleomycin have been reported, no bleomycin or deglycobleomycin analogue having enhanced DNA cleavage activity has yet been described. The successful synthesis of a deglycobleomycin on a solid support has permitted the facile solid-phase synthesis of 108 unique deglycobleomycin analogues through parallel solid-phase synthesis. Each of the deglycobleomycin analogues was synthesized efficiently; the purity of each crude product was greater than 60%, as determined by HPLC integration. The solid-phase synthesis of the deglycobleomycin library provided near-milligram to milligram quantities of each deglycobleomycin, thereby permitting characterization by (1)H NMR and high-resolution mass spectrometry. Each analogue demonstrated supercoiled plasmid DNA relaxation above background cleavage; the library included two analogues that mediated plasmid relaxation to a greater extent than the parent deglycobleomycin molecule.